This invention relates to smoking articles and smoking materials, and more particularly to such articles and materials containing a catalyst for the oxidation to carbon dioxide of carbon monoxide in the smoking decomposition products of the smoking material.
Many substances are known to act as catalysts for the conversion of carbon monoxide to carbon dioxide. For example, in Chem. Commun., 1999, 1373-1374, Taylor et al disclose the use of a mixed oxide of copper and zinc for this purpose; U.S. Pat. No. 4,839,327 discloses catalysts for oxidising carbon monoxide to carbon dioxide comprising an ultra-fine deposit of gold upon metal oxides including MnO2, Fe2O3, CuO, CuMnO2, Al2O3, SiO2, and TiO2; U.S. Pat. No. 5,068,217 discloses a catalyst comprising gold deposited on a porous ceramic carrier material which contains Fe2O3; US-2003/099586 discloses a catalyst comprising gold on a carrier of Fe2O3; and U.S. Pat. No. 4,698,324 describes the deposition of gold or a mixture of gold with a catalytic metal oxide (Cr2O3, MnO, NiO, Fe2O3, Co3O4, CuO) on a carrier of silica, alumina or magnesia.
Several proposals have been made to incorporate catalysts in smoking articles and smoking materials so that carbon monoxide in the smoking decomposition products is converted to carbon dioxide. For example, international patent publication WO 2004/002247 discloses several catalysts for incorporation in a cigarette. One such catalyst comprises zinc aluminate. Another comprises gold deposited upon a rare earth oxide such as cerium oxide. US-2003/0075193 discloses a smoking material that contains a catalyst in the form of nanoparticles of metal oxides (such as Fe2O3, CuO, TiO2, CeO2, Ce2O3, Al2O3, or Y2O3) doped with Zr, and MnO2 doped with Pd. Chinese patent specification CN-1464058 discloses a complex catalyst system for reducing the amount of carbon monoxide in tobacco smoke. The system has three active components (Au, Pt and Pd) and at least 2 promoters (Fe, Cu and, optionally, Zn) on a support made of alumina, silica, bentonite or molecular sieve material.
When a catalyst is incorporated in a smoking article, the catalyst can become rapidly de-activated or poisoned by humidity or other substances in the smoke. In addition, the presence of a catalyst in the smoking material or smoking article can adversely affect the flavour of the smoke. Furthermore, many catalysts are only effective at temperatures higher than those at which tobacco smoke is inhaled from a cigarette.
Accordingly, many catalysts that are effective in catalysing the conversion of uncontaminated CO to CO2 in fact prove to be in effective for use in catalysing the conversion in tobacco smoke, as revealed by testing the efficacy of the catalysts under conditions that simulate true smoking conditions.
The present invention is based upon the selection of certain catalysts containing gold for use in oxidising carbon monoxide to carbon dioxide in the decomposition products of smoking material. The selected catalysts are referred to in this specification as “catalysts of the invention”.